This one is, primarily, for all the people responsible for ensuring a WordPress site remains available and running well. “Systems” people if we must name them. If you’re a WordPress developer you might want to ride along on this one as well so you and the systems or DevOps team can be speaking a common language when things go bad. Often times, systems people will immediately blame developers for writing bad code but the two disciplines must cooperate to keep things running smoothly, especially at scale. It’s important for systems AND developers to understand how code works and scales on servers.
What I’m about to cover is some common performance issues that I see come up and then be misdiagnosed or “fixed” incorrectly. They’re the kind of thing that causes a WordPress site to become completely unresponsive or very slow. What I cover may seem obvious to some, and they are certainly very generalized, but I’ve seen enough bad calls to know there are a number of people out there that get tripped up by these situations. None of the issues are necessarily code related nor are they strictly WordPress related, they apply to many PHP based apps; it’s all about how sites behave at scale. I am going to explore WordPress site performance issues since that’s where my talents are currently focused.
In all scenarios I am expecting that you are running something getting a decent amount of traffic at the server(s). I am assume you are running a LEMP stack consisting of Linux, Nginx, PHP-FPM and MySQL. Maybe you even have a caching layer like Memcached or Redis (and you really should). I’m also assuming you have basic levels of visibility into the app using something like New Relic.
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